Transmission Temperature Sensing and Control

ABSTRACT

As one example approach, temperature indications from transmission actuators are used to control the actuators and transmission shifting. For example, temperature differences among the different actuators can be used to provide improved relative timing and actuation levels and thus improved shifting control.

BACKGROUND AND SUMMARY

Vehicle propulsion systems typically include a transmission fortransferring mechanical work from a propulsion device such as aninternal combustion engine or electrically powered motor to a drivewheel of the vehicle. These transmissions can be configured to provide aplurality of selectable gear ratios between an input shaft for receivingthe mechanical work and an output shaft for delivering the mechanicalwork to the drive wheel. A transmission controller can be provided forselecting the appropriate transmission gear ratio. In some examples, thecontroller can adjust the transmission gear ratio via one or moretransmission actuators that can manipulate the various transmissionelements for effectuating the selected gear ratio by way of a clutch orother suitable device.

One approach for controlling the actuation signal provided to thesetransmission actuators is described by U.S. Pat. No. 6,262,556. Thisapproach describes how the actuation signal that is provided to anactuator during a transmission shift can be adjusted based on a measuredtemperature of the transmission's hydraulic fluid. In particular, U.S.Pat. No. 6,262,556 describes how a temperature measured at thetransmission sump can be used to select the actuation signal.

However, the inventors herein have identified several issues with theabove approach. As one example, the inventors have recognized thatmeasuring the temperature of the hydraulic fluid at only a singlelocation, such as by way of a temperature sensor, provides only alimited indication of transmission temperature during some conditions.For example, during warm-up of the transmission after a cold start,thermal gradients may exist between different regions of thetransmission. Furthermore, if the temperature sensing capability of thetemperature sensor becomes degraded over time, the transmission may beimproperly controlled. Further still, a dedicated transmissiontemperature sensor can add additional cost and complexity to thetransmission.

As such, the inventors herein have addressed some of the above issues bya propulsion system for a vehicle, comprising a propulsion deviceconfigured to provide mechanical work via a crankshaft; a transmissionhaving an input shaft coupled with the crankshaft and an output shaft,wherein said transmission includes a plurality of selectable gear ratiosbetween the input and output shaft; at least one drive wheel coupledwith the output shaft; an actuation device configured to adjust theselected gear ratio of the transmission; and a control system configuredto adjust an electrical signal provided to the actuation device toobtain an indication of a temperature dependent electrical parameter ofthe actuation device and to adjust the selected gear ratio oftransmission by varying the signal provided to the actuation device inresponse to said indication.

In this way, each actuator of the transmission can be used to provide anindication of temperature, thereby providing a distributed indication oftransmission temperature even where temperature gradients exist. Thus,the actuation signal provided to each actuator can be controlled inresponse to their respective temperature indication and the timing ofthe actuation as well as the transmission shift points can be moreaccurately controlled by the transmission control system.

As another example, a method of operating a transmission of a vehiclepowertrain including at least a first and a second actuator is provided.The method comprises performing a transmission shift by actuating afirst transmission element via the first actuator and actuating a secondtransmission element via the second actuator; and varying a timing ofactuation of the first transmission element relative to the secondtransmission element based on an indication of a temperature dependantelectrical property of at least one of the first actuator and the secondactuator.

In this way, two or more actuators of the transmission can becoordinated based on an indication of temperature obtained from antemperature dependant electrical parameter of one or more actuators,such as an electrical resistance of the actuator coil, for example.Furthermore, in some examples, the actuators can be coordinated based ona comparison of their respective temperature indications, therebyenabling smoother and more efficient transmission shifts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an example vehicle powertrainincluding a transmission having a plurality of hydraulic actuators.

FIGS. 2A and 2B show a schematic depiction of an example electriccircuit for a hydraulic actuator of a transmission.

FIGS. 3A-3C show flow charts depicting example approaches foridentifying temperature at the transmission actuator.

FIGS. 4A and 4B show flow charts depicting example approaches foradjusting the temperature indication obtained from an actuator basedupon an estimated temperature deviation from the fluid temperature.

FIG. 5 is a graph showing how the actuator temperature can be increasedin response to an actuation.

FIG. 6 is a graph showing how actuator control can vary with actuatortemperature.

FIGS. 7A and 7B show flow charts depicting example approaches forcontrolling the actuator in response to the temperature of the actuatoror the temperature at other thermally related actuators.

FIG. 8 is a graph shown how transmission shift points can vary withactuator temperature.

DETAILED DESCRIPTION

FIG. 1 a schematic depiction of an example vehicle powertrain 100including an internal combustion engine 110, transmission 120, and atleast one driven wheel 130 communicating with a ground surface 132.Engine 110 includes one or more combustion chambers or cylindersindicated at 112. A mechanical output of engine 110 can be provided viaa crankshaft 144. Note that engine 110 is merely one type of propulsiondevice that can be configured to provide mechanical work to a drivewheel of the vehicle. In other examples, engine 110 can be replaced withan electrically powered drive motor. In still other examples, engine 100can be included with an electrically powered drive motor, such as wherevehicle powertrain 100 is configured as a hybrid electric vehicle (HEV).

Transmission 120 includes an input shaft 142 coupled with crankshaft 144of engine 110 via a torque converter 148. Torque converter 148 can beprovided in some examples for varying the rigidity of the couplingbetween crankshaft 144 and input shaft 142. Transmission 120 alsoincludes an output shaft 146 coupled with drive wheel 130. Thus, amechanical output provided by engine 110 can be delivered to drive wheel130 via transmission 120 and/or torque converter 148.

Transmission 140 can include one or more actuators for controlling theengagement and disengagement of various transmission elements. Some ofthese actuators are shown schematically at 122, 124 and 126. As onenon-limiting example, some of these actuators may be configured ashydraulic actuators for engaging or disengaging one or more clutches ofthe transmission. These clutches may be hydraulically actuated by way ofa hydraulic fluid as shown in greater detail in FIG. 2A. Furthermore,these clutches can be used, for example, to enable an adjustment of thetransmission operating state, including the gear ratio provided betweeninput shaft 142 and output shaft 146. Actuators 122, 124, and 126 caninclude an electromechanical actuator coil (e.g. a solenoid) for openingand closing a hydraulic valve for controlling the pressure applied tothe transmission clutches as also shown in FIG. 2A. In some examples,transmission 140 may also include a temperature sensor indicated at 128,which can provide an indication of transmission temperature tocontroller 150. However, in some examples, temperature sensor 128 may beomitted from transmission 120.

The various actuators, including 122, 124, and 126, can be controlled bycontroller 150. Controller 150 can include a computer or an electroniccontrol unit (ECU) comprising an input/output interface (152), a centralprocessing unit (CPU) 154, and memory 156. Note that the memory mayinclude read-only memory (ROM), random access memory (RAM), and/orkeep-alive memory (KAM). Each of the input/output interface, CPU, andmemory can communicate via a data bus.

Controller 150 can obtain powertrain operating condition informationfrom various sensors associated with the powertrain and can send variouscontrol signals to the powertrain to control operation of the engine,torque converter, and/or transmission via interface 152. For example,interface 152 can send adjust the position of the various transmissionactuators by applying an electrical current to their respective actuatorcoils. FIG. 2B shows an example circuit for controlling an exampletransmission actuator that can communicate with controller 150. Thecombination of controller 150 and the various mechanical and electricalsubsystems that can be used for carrying out the commands of controller150 are collectively referred to herein as the powertrain controlsystem. Furthermore, it should be appreciated that the control systemcan include other controllers and electrical and/or mechanicalsubsystems beyond those described herein.

Controller 150 can also receive engine operating conditions from engine110, including an indication of the speed of crankshaft 144. Controller150 can also receive an input from one or more user input devices. Forexample, a vehicle operator can provide an input via pedal 162, whichmay be configured as an accelerator pedal, a brake, or a clutch.Furthermore, controller 150 can receive input from the vehicle operatorvia a transmission gear selector 164. In response to these variousinputs, the control system including controller 150 can adjust theoperating state of engine 110, torque converter 148, and transmission120. For example, controller 150 can adjust the lock-up state of torqueconverter 148 and/or the selected gear ratio of transmission 120 inresponse to input received from user input devices 162 and 164.

FIGS. 2A and 2B show an example transmission actuator and respectiveactuator circuit that may be operated by controller 150 to adjust anoperating state of the transmission. Referring specifically to FIG. 2A,an example transmission actuator 200 is described. Actuator 200 can beused as one of actuators 122, 124, and 126 shown schematically inFIG. 1. Actuator 200 can include a hydraulic valve including a valvebody 210 defining an internal region 220. A valve arm 234 can include aplurality of valve seals indicated generally at 236 for partitioning ordefining different sub-regions within region 220.

Valve arm 234 can be fixedly coupled with a valve armature. The positionof valve armature 232 can be varied relative to valve body 210 byactuator coil 235, thereby causing valve arm 234 to translate relativeto valve body 210. Thus, actuator coil 235 and valve armature 232 inthis particular example form a solenoid. As one example, controller 150can vary the electrical power applied to coil 235, for example, byvarying the current and/or voltage that is applied across nodes 262 and264, in order to cause valve arm 234 to translate relative to valve body210. In this particular example, armature 232 and hence valve arm 234can be biased in a particular direction by a spring indicated at 233.However, in other examples, actuator 200 can include two coils thatprovide opposing forces. Regardless of the particular configuration,controller 150 can adjust the position of valve arm 234 by adjusting thevoltage or current that is applied to coil 235.

A hydraulic fluid can be provided to internal region 220 of valve 200via a hydraulic passage 224. As one example, the hydraulic fluid that isprovided to internal region 200 via passage 224 can be pressurized by ahydraulic pump or other suitable pressurization device. Hydraulic fluidcan also be removed from internal region 200 via hydraulic passage 222.In some examples, hydraulic passage 222 may include a valve (not shown)that can be controlled by controller 150 to regulate the flow ofhydraulic fluid leaving internal region 220. Internal region 220 caninclude additional hydraulic passages 226 and 228 that communicate withactuator arm assembly 240. Assembly 240 includes an actuator arm 244having a sealing armature 246 that defines two separate internal regionsof assembly 240 as indicated at 242 and 243.

Thus, region 242 can selectively communicate with region 220 via passage226 and region 243 can selectively communicate with region 220 viapassage 228 depending on the position of valve seals 236 within region220 relative to the position of the various hydraulic passages. Forexample, during a first position of valve arm 234 and valve seals 236,region 242 can be hydraulically isolated from region 220 and during asecond position, region 243 can be hydraulically isolated from region220. As pressurized hydraulic fluid is provided to region 220 viapassage 224, the hydraulic pressure in each of regions 242 and 243 canbe varied relative to each other by adjusting the position of valve arm234. The difference in hydraulic pressure between regions 242 and 243causes actuator arm 244 and sealing armature 244 to translate relativeto assembly 240. In this way, a transmission element 250 thatcommunicates with actuator arm 244 can be adjusted by the control systemby varying the voltage and/or current that is applied to nodes 262 and264. Note that the particular actuator described with reference to FIG.2A is merely one example of a hydraulic actuator for a transmission andthat other suitable actuators may be used.

FIG. 2B shows an example actuator driver circuit 280 that can utilizedby controller 150 to adjust the voltage and/or current applied at nodes262 and 264, thereby facilitating the actuation of actuator 200. Notethat circuit 280 and controller 150 can collectively be referred to asthe control system. Furthermore, circuit 280 is merely an example of acircuit that may be used for actuator coil 235 and that other suitablecircuits may be used.

As indicated at 274, controller 150 can prescribe a current that is tobe applied to the actuator coil. As indicated at 273, an error 273between the actual current applied to the coil as indicated 266 and theprescribed current 274 can be provided to pulse width modulator 270,which can provide an output signal 268 to transistor 278. Transistor 278can act as a switch in response to signal 268 to enable a potential tobe applied across resistor 276 and coil 235 between ground (lowerpotential) and a higher potential of an applied energy source such as abattery denoted as V_BATT. The resistance across the transistor when itis on (i.e. driven by PWM 270 is indicated as R_DS_ON. A diode 288 canbe provided between the higher potential side of transistor 278 andV_BATT. The resistance across resistor 276, denoted as R_SENSE, and thepotential across resistor 276 can drive op amp 282 to provide anindication of the actual current (I_COIL) applied to coil 235.Similarly, an indication of the voltage across coil 235 (V_COIL) can beobtained from op amp 284 as indicated at 286. As another example, thevoltage across coil 235 can be obtained from the difference between thevoltages at nodes 262 (V_262) and 264 (V_264). As yet another example,the voltage across the coil can be obtained from individual measurementsby the following equation:

V_COIL=V _(—)262−(I_COIL*R_SENSE)−(I_COIL*R_DS_ON).

Regardless of the particular configuration of the actuator drivercircuit, controller 150 can adjust the level of current that is appliedto the actuator coil (I_COIL) and can obtain an indication of theresulting coil voltage (V_COIL). Alternatively, the controller canadjust the voltage applied across the coil (V_COIL) and can obtain anindication of the applied current (I_COIL).

FIGS. 3A-3C show several flowcharts depicting example methods foridentifying a temperature of a transmission actuator coil, which can beused by the control system as an indication of transmission fluidtemperature in the vicinity of the actuator. In response to theindication of temperature obtained from the actuator coil, the controlsystem can adjust actuator operation so that adjustments of transmissionelements can be properly coordinated across a variety of thermalconditions. For example, where the physical properties of the hydraulicfluid, such as fluid viscosity and/or density, change with variations intemperature, the transmission actuators can respond differently to agiven current that is applied by the control system to cause anadjustment of transmission operating state.

In each of the different approaches described with reference to FIGS.3A-3C, a temperature dependent electrical property of the actuator coilcan be used to identify the temperature at the actuator coil. As oneexample, the electrical property of the coil can include an electricalresistance of the coil.

As one example, the approach described with reference to FIG. 3A can beutilized where a temperature indication is to be obtained from theactuator coil based on actuator coil resistance without initiating anactuation of a transmission element. At 310, it can be judged whether atemperature indication is to be identified at the actuator. For example,the control system can judge that the temperature at the actuator is tobe identified based on a prescribed temperature sampling frequency. Asanother example, the control system can forego obtaining a temperaturemeasurement from the actuator coil when it is being operated (e.g.energized) to provide actuation of a transmission element. As yetanother example, the control system can identify the temperature at theactuator coil before an actuation of a transmission element is to beinitiated. If the answer at 310 is yes, the routine can proceed to 312.Alternatively, if the answer at 310 is no, the routine can return.

At 312, the control system can apply a current the actuator coil that isless than a threshold current for actuating the actuator coil (i.e.threshold actuating current). For example, referring also to FIG. 2, thecontrol system can prescribe a current to be applied to the coil asindicated at 274. Note that the threshold actuating current describedherein can also vary with the temperature of the surrounding hydraulicfluid. For example, variations in fluid viscosity and/or density thatresult from changing fluid temperatures can cause the thresholdactuating current to increase or decrease relative to a referenceactuating current. As such, the threshold actuating current can beidentified by the control system based on feedback from previouslyobtained actuator coil or transmission fluid temperature indications aswill be described with reference to FIGS. 3 and 4.

In response to the current applied to the actuator coil (i.e. I_COIL),the control system can measure the resulting voltage (V_COIL) developedacross the actuator coil as indicated at 314. At 316, the resistance ofthe actuator coil can be calculated based on the applied current(I_COIL) and measured voltage as directed by Ohm's law. For example, thecontrol system may calculate the actuator coil resistance (R_COIL) basedon the following equation: R_COIL=V_COIL/I_COIL. As another example, thecontrol system can utilize a look-up table or map stored in memory toidentify the resistance of the coil based on the applied current andmeasure voltage. While the approach described at 312 and 314 utilizes anapplied current and response voltage, in other examples, a voltage canbe applied across the actuator coil and the resulting current can bemeasured.

At 318, the actuator coil temperature can be calculated by the controlsystem based on resistance obtained at 316 and the thermal properties ofthe coil. As one example, where the actuator coil comprises copper, thecoil temperature (T_COIL) can be calculated based on the followingequation: T_COIL=T_REF+((R_COIL−(R_REF)/(R_REF*α_REF)), where R_REF isthe resistance of the actuator coil at a reference temperature (T_REF)and α_REF is the temperature coefficient of resistance for the coilmaterial at the reference temperature. For example, where the actuatorcoil comprises copper, α is equal to approximately 0.004041 at areference temperature of 20 degrees Celsius and α has the dimensions ofan inverse temperature. In some examples, the control system can utilizea look-up table or map stored in memory to identify the coil temperaturebased on a give coil resistance or it can calculate the coil temperatureas described by the previous equation.

As indicated at 320 and 322, the timing of a subsequent actuation of theactuator and/or a profile of the current applied to the actuator duringthe actuation can be varied responsive to the indication of coiltemperature identified at 318. Referring also to FIG. 5, the timing atwhich the actuator is actuated can be controlled by the control systemby varying the timing at which the current applied at the coil reachesor exceeds the threshold actuation current of the coil. In other words,the control system can vary the prescribed current provided at 274. Forexample, the control system can advance or retard the timing at whichthe applied current is controlled to attain or exceed the thresholdactuating current as shown in FIG. 6. Further, the profile of thecurrent applied at the coil can include the current gain (e.g. themagnitude of the current) as well as the rate of increase and/ordecrease of the applied current. For example, the control system canincrease or decrease the rate of change of the applied current and/orthe magnitude of the applied current in response to actuator coiltemperature. In some examples, the control system can utilize a look-uptable, a, or an algorithm stored in memory to select a timing for thecurrent and current profile to be supplied to the actuator coil based onthe temperature of the surrounding fluid indicated by the coil. Forexample, FIG. 8 shows how the transmission shift points can be adjustedby the control system responsive to actuator temperature. In this way,where the physical properties (e.g. viscosity, density, etc.) of thesurrounding transmission fluid vary with temperature, the actuation ofthe transmission element can be suitably timed by identifying thetemperature of the fluid and adjusting the actuator command currentaccordingly. Finally, the routine can return.

In contrast to the approach described with reference to FIG. 3A, theapproach of FIG. 3B can be utilized where a temperature indication is tobe obtained from the actuator in coordination with a subsequentactuation, while still retaining the ability to adjust the timing of theactuation as directed by the commanded current timing and the currentprofile applied to the coil.

At 330, it can be judged whether to identify the temperature at theactuator. The operation at 330 can be the same as the operationdescribed at 310. For example, the control system can choose to identifythe temperature of the actuator just before the actuator is to beoperated to actuate a transmission element. If the answer at 330 is yes,the routine can proceed to 332. Alternatively, if the answer at 330 isno, the routine can return.

At 332, an initial current can be applied to the actuator coil by thecontrol system that is less than the threshold coil actuation current.In other words, a current that is insufficient to cause the actuator toactuate the transmission element can be applied to the coil. In responseto the applied current, the voltage can be measured as indicated at 334,the actuator resistance can be identified as indicated at 336, and theactuator coil temperature can be determined at 338, for example, aspreviously described with reference to operations 314, 316, and 318,respectively.

In response to the indication of temperature obtained at 338, thecurrent applied to the actuator coil at 332 can be increased to at leastthe threshold coil actuation current to initiate actuation, as indicatedat 340. The timing at which the applied current attains the thresholdactuation current can be varied at 342 in response to the temperatureindication obtained at 340. For example, the control system can advanceor retard the timing at which the applied current is controlled toattain or exceed the threshold actuation current. Furthermore, theprofile of the applied current including the rate of change of thecurrent and the current magnitude can be varied at 344 responsive to theindication of temperature obtained at 340. For example, the controlsystem can increase or decrease the rate of change of the appliedcurrent and/or the magnitude of the applied current in response toactuator coil temperature. In this way, the actuator can be controlledbased upon the actuator temperature which is indicative of transmissionfluid temperature in the vicinity of the actuator. Finally, the routinecan return.

In contrast to the approach described with reference to FIG. 3B, theapproach of FIG. 3C can be utilized during the initial stages of theactuation process where a temperature indication is obtained from theactuator coil before it begins to increase in temperature due to theapplied actuation current, while still retaining the ability to adjustthe current profile applied to the coil. For example, the control systemcan measure the V_BATT or V_262 and I_SOL at the start of the on cycleof PWM 270 to determine the bulk temperature of the actuator coil fromthe in-rush current before the current causes additional heating of thecoil. Thus, the current and voltage of the coil can be obtained duringthe period indicated at 550 of FIG. 5. Note that one disadvantage of theapproach described by FIG. 3C is that the initiation of the actuationmay not be variable in at least some examples based on the temperatureidentified during the same actuation as is the case with the approach ofFIG. 3B. However, the actuation timing can be adjusted during subsequentactuations based on the indication of actuator temperature obtained fromthe previous actuation.

At 350, it can be judged whether to identify the temperature of theactuator. As one example, the control system can obtain the actuatortemperature during the initial stages of some or all of the actuationsto enable control of the current provided to the actuator coil. In someexamples, the operation at 350 can be the same as previously describedby operations 310 and 330. If the answer at 350 is yes, the routine canproceed to 352. If the answer at 350 is no, the routine can return.

At 352, a current can be applied to the actuator coil that is at leastas great as the actuation current. At 354, 356, and 358, the temperatureof the actuator coil can be identified based on the applied current at352, for example, as previously described by operations 314, 316, and318, respectively. At 360, the profile of the applied current can beadjusted from the current applied at 352 in response to the indicationof temperature obtained at 358. For example, the control system canincrease or decrease the rate of change of the applied current and/orthe magnitude of the applied current in response to actuator coiltemperature.

Thus, FIGS. 3A-3C provide several approaches that may be used to obtainan indication of the actuator coil temperature and/or the temperature ofthe surrounding transmission fluid, whereby the timing of the actuationas well as the actuation force can be adjusted by varying the timing ofthe applied current and the profile of the applied current,respectively.

FIG. 4A and 4B show flowcharts depicting example methods for adjustingthe temperature indication obtained from the actuator based on anestimation of a temperature deviation between the fluid temperature andthe actuator temperature that can occur due to a previous actuation.Since the current applied to the actuator during an actuation eventpasses through the actuator coil, which has an inherent resistance, theactuator can increase in temperature and therefore deviate from thefluid temperature. Thus, if the actuator temperature is obtained by oneor more of the approaches previously described by FIGS. 3A-3C, theactuator coil can provide a false indication of fluid temperature.

The approach of FIG. 4A adjusts the temperature identified from theactuator based on an estimate of the temperature deviation or differencebetween the temperature of the surrounding fluid and the temperature ofthe actuator based upon operating parameters of the previous actuation,while the approach of FIG. 4B obtains multiple indications oftemperature from the actuator coil over a period of time after theactuation to estimate the temperature deviation.

Referring specifically to FIG. 4A, at 410, it can be judged whether toidentify the temperature at the actuator. This decision can be the sameas those described with reference to FIGS. 3A-3C. If the answer at 410is no, the routine can return. Alternatively, if the answer at 410 isyes, the routine can proceed to 412. At 412, a current can be applied tothe actuator coil and a temperature indication of the coil can beobtained as previously described with reference to one of the approachesof FIGS. 3A-3C. At 414, it can be judged whether the time after anactuation of the actuator has been terminated (e.g. when the appliedcurrent has been removed or reduced below the actuation currentthreshold) is greater than a threshold. As one example, the controlsystem can select a time threshold based on operating parameters of theactuator such as actuation time, applied current, transmission fluidtemperature, etc. This time threshold can represent a sufficient periodof time for the actuator temperature to return to substantially the sametemperature as the fluid after the actuation has been terminated. If theanswer at 414 is yes, the routine can proceed to 424 and 426, where theindication of actuator coil temperature that was obtained at 412 can beused to adjust the subsequent actuation current and/or the profile ofthe applied current as previously described with reference to FIGS.3A-3C.

Alternatively, if the answer at 414 is no (i.e. the time after actuationis less than the threshold), the temperature indication obtained at 412can be adjusted at 416 based on an estimated deviation of the actuatorcoil temperature from the surrounding fluid temperature. For example, at416, the control system can estimate a temperature deviation between theactuator coil and the surrounding transmission fluid based on variousoperating parameters of the previous actuation and the amount of timesince the previous actuation. These operating parameters may include theduration of the previous actuation, the level of current provided to theactuator over the actuation period, and the temperature of thetransmission fluid, which may be based on a previous temperatureindication provided by the actuator, a temperature indication providedby other transmission actuators or a transmission fluid temperaturesensor. Thus, the temperature deviation during a period after a previousactuation as indicated for example at 560 of FIG. 5, can be estimated bythe control system.

At 418, the coil temperature indication obtained at 412 can be adjustedbased on the estimated temperature deviation obtained at 416. Forexample, the control system can subtract the estimated temperaturedeviation from the temperature indicated by the actuator coil to obtaina better indication of the temperature of the transmission fluid in thevicinity of the actuator.

At 420 and 422, the timing of a subsequent actuation and/or the currentprofile provided to the actuator coil during the subsequent actuationcan be varied in response to the adjusted actuator coil temperatureobtained from 418. Note that the operations at 420 and 422 can be thesame as the operations of 320 and 322 in the case where operation 412utilized the approach of FIG. 3A, or they may be the same as theoperations of 342 and 344 in the case where operation 412 utilized theapproach of FIG. 3B, or may be the same as operation 360 in the casewhere operation 412 utilized the approach of FIG. 3C. Finally, from 422or 426, the routine can return.

Referring now to FIG. 4B, at 430, it can be judged whether thetemperature at the actuator is to be obtained by the control system. Ifthe answer at 430 is no, the routine can return. Alternatively, if theanswer at 430 is yes, the routine can proceed to 432. At 432, it can bejudged whether the time after actuation of the actuator has beenterminated is greater than a threshold. The decision at 432 can be thesame as the decision at 414. For example, if the answer at 432 is yes,the routine can proceed to 444 and 446, which can be the same asoperations 424 and 426, respectively. Alternatively, if the answer at432 is yes, the routine can proceed to 434. At 434, a current can beapplied to the actuator coil a plurality of times in order to obtain aplurality of temperature measurements over a period of time after theactuation has terminated, for example, as described by the approach ofFIG. 3A. For example, as the actuator temperature returns to thetemperature of the fluid after the actuation has been terminated, thecontrol system can obtain two or more indications of temperature.

From the temperature measurements obtained at 434, at 436, the controlsystem can estimate the deviation of actuator coil temperature from thesurrounding fluid temperature based on a change in the temperatureindicated by the plurality of temperature measurements. As one example,where the plurality of temperature measurements indicate a largertemperature difference between each other, it can be inferred that thetemperature deviation is larger than if the temperature measurements aremore similar. The control system can utilize a look-up table or a mapstored in memory to estimate the temperature deviation between theactuator coil and the surrounding fluid based on a temperaturedifference between two or more temperature measurements performed afterthe actuation event has been terminated. Furthermore, in some examples,the control system may utilize some or all of the operating parametersof the previous actuation (e.g. as described at operation 416) toimprove the accuracy or precision of the estimated temperaturedeviation.

The operations at 438, 440, and 442 may then be performed, whereby thetemperature indicated by the last measurement of the plurality oftemperature measurements obtained at 434 can be adjusted based on theestimated temperature deviation obtained at 436, and the timing of asubsequent actuation and/or the current profile provided to the actuatorduring the subsequent actuation can be varied in response to theadjusted temperature indication obtained at 438. Note that theoperations at 438, 440, and 442 can be the same as those previouslydescribed at 418, 420, and 422, respectively.

In this way, the control system can utilize one or more of theapproaches of FIGS. 3A-3C to obtain an indication of actuatortemperature and adjust this indication by an estimated temperaturedeviation obtained by one or more of the approaches of FIGS. 4A and 4B,whereby the adjusted temperature indication can be used to control thecurrent that is supplied to the actuator coil during a subsequentactuation event. However, in some examples, the control system canutilize temperature indications obtained from the actuator coil onlyafter the actuator has returned to the temperature of the surroundinghydraulic fluid without utilizing a temperature adjustment.

FIG. 5 shows a graph depicting an example of how the actuator coiltemperature can deviate from the temperature of the surroundingtransmission fluid due to a coil actuation event. In this particularexample, the horizontal axis of the graph shows an indication of timeand the vertical axis shows an indication of actuator coil temperature.Furthermore, the temperature of the fluid (e.g. the transmission oil) inthe vicinity of the actuator is depicted as a horizontal broke line. Thegraph shows how the actuator coil temperature indicated at 500 caninitially be the same as the temperature of the fluid. As indicated at520, the actuator coil is then supplied with power (e.g. an electricalcurrent) to cause actuation of an element of the transmission. Inresponse to the application of electrical energy to the actuator coil,the temperature of the actuator can begin to increase as indicated at540. When the electrical energy that is supplied to the coil is finallyremoved as indicated at 530, such as after the actuator has completedactuation of the transmission element, the temperature of the coil cansubsequently return to the transmission fluid temperature over a periodof time indicated by 560.

As previously described with reference to FIGS. 4A and 4B, thetemperature indication obtained from the actuator can be adjusted basedon an estimated temperature deviation caused by a previous actuation.However, in the example shown in FIG. 5, during the periods indicated at510 and 570, an adjustment of the temperature indication is not requiredsince the temperature of the actuator coil is substantially the same asthe surrounding fluid temperature. For example, the threshold period oftime judged at 410 and 430 can be at least after the beginning of theperiod indicated by 570. However, during the period indicated by 560,the temperature indication obtained from the actuator can be adjusted toaccount for the deviation between the actuator coil temperature and thetemperature of the surrounding fluid.

The example shown in FIG. 5 also demonstrates how during a relativelyshort period of time after power is supplied to the actuator coil, asindicated at 550, for purposes of actuating a transmission element, thetemperature of the coil is still substantially the same as thetemperature of the fluid. Thus, the temperature of the actuator coil canbe obtained during the period indicated at 550, for example as describedwith reference to the approach of FIG. 3C, without requiring anadjustment of the temperature indication since there is substantially nodeviation between the actuator temperature and the temperature of thesurrounding fluid.

FIG. 6 shows a graph depicting an example of how the current applied tothe transmission actuators can vary with the temperature of thetransmission fluid temperature. In this particular example, thehorizontal axis of the graph shows an indication of time and thevertical axis shows an indication of actuator coil temperature andactuation current. Beginning on the left side of the graph, initially,the fluid temperature in the vicinity of two separate and remoteactuators are substantially the same. For example, during a cold startbefore the transmission has started warming up, the temperature of thetransmission fluid in all locations of the transmission can be equal,such as at ambient. However, as time progresses (e.g. during warm-up,the temperature of the fluid in different regions of the transmissioncan be heated at different rates. For example, the fluid temperature inthe vicinity of a first actuator is indicated at 612 and the fluidtemperature in the vicinity of a second actuator is indicated at 614. Asshown in FIG. 6, the temperature difference between the two fluidtemperatures can differ by a temperature differential indicated at 616.Note that the temperature differential can also decrease, for example,as the temperature of the transmission approaches its steady stateoperating temperature.

FIG. 6 also shows how the minimum actuation current for each of theactuators can vary with their respective temperature. In other words, asthe temperature of the first actuator increases as indicated by 612, theminimum actuation current for the first actuator can also change asindicated at 622. In this particular example, the minimum actuationcurrent decreases with increasing temperature of the actuator and/orsurrounding fluid, for example, as the viscosity of the transmissionfluid also increases with increasing temperature. However, in otherexamples, the minimum actuation current can also increase withincreasing temperature of the actuator and/or surrounding fluid. FIG. 6further shows how the minimum actuation current for the second actuatorcan also vary as indicated at 614 responsive to the temperature of thesecond actuator indicated at 614. Thus, the difference between theminimum actuation current of the first and second actuators can beobserved as the difference between 622 and 624.

As previously described with reference to FIGS. 3 and 4, the time atwhich the minimum actuation current is applied at the actuator and/orthe current profile applied to the actuator can be varied in response tothe temperature indication obtained from the actuator. FIG. 6 also showshow the magnitude commanded actuation current can be varied for thefirst and second actuators as the temperature of the actuators varies.For example, the current applied to the first actuator is indicated at632 and the current applied to the second actuator is indicated at 634for a plurality of actuation events indicated at 642-648. Actuationevents 642-648 can represent transmission state changes whereby atransmission gear is activated and/or deactivated by the actuation oftwo or more transmission elements. Note that while actuation of only twoactuators is described with reference to the example of FIG. 6, itshould be appreciated that more or less actuators can be coordinated tovary an operating state of the transmission.

In this particular example, the various actuation events indicated at642-648 for the given temperature conditions indicated at 612 and 614for the two actuators can be used to illustrate how the relative timingat which the actuation current is applied to the actuators can be variedin response to the temperature at each of the actuators. For example, asindicated at 642, the actuation current is first applied to the firstactuator before the second actuator, while at other conditions, asindicated at 648, the actuation current can be first applied to thesecond actuator before the first actuator. Additionally, it can beobserved that the relative timing for the application of the actuationcurrent between the two actuators can be advanced or retarded based ontheir respective temperature conditions. Furthermore, FIG. 6 also showshow the magnitude of the applied actuation current can also be variedwith temperature. For example, actuation event 642 shows how the currentapplied to the first actuator can be greater than the current applied tothe second actuator, while during a different actuation event (e.g. at adifferent temperature condition), the current applied to the secondactuation can be greater than the current applied to the first actuator.FIG. 6 shows how the actuation current that is applied to each of theactuators can be controlled to be at least greater than the minimumactuation current for the respective actuator, thereby ensuring thatactuation occurs as commanded by the control system. Further still,while not shown in FIG. 6, the rate of increase or decrease of theapplied current can be varied for each of the actuators in response totheir respective temperature conditions as obtained by at least one ofthe approaches previously described with reference to FIGS. 3 and 4.

In this way, by adjusting the timing at which the current is applied tothe actuator and the profile of the applied current including themagnitude and rate of change during actuation, each actuator can becontrolled in response to their specific temperature indication. Thus,the timing and profile of the actuation current that is applied to theactuators can be varied relative to each other as their operatingtemperatures and hence the temperature of their surrounding fluidsdeviate from each other.

FIGS. 7A and 7B show flowcharts depicting example methods for adjustingan operating state of the transmission by adjusting one or moreactuators based upon their respective temperature (e.g. as shown in FIG.7A) and/or based upon the temperature of other actuators that arethermally related to the adjusted actuator.

Referring specifically at FIG. 7A, at 710, the operating conditions ofthe vehicle powertrain can be assessed. For example, the control systemcan identify the various operating conditions of the engine andtransmission based on the various sensors described with reference toFIG. 1, including the temperature obtained from the various actuators,transmission input speed, transmission output speed, engine speed,ambient conditions, and input received from the vehicle operator via oneor more user input devices.

At 712, it may be judged whether to adjust the operating state of thetransmission based on the operating conditions identified at 710. Forexample, the control system may judge that the transmission operatingstate is to be adjusted in response to input receive from the vehicleoperator including a shift request and/or a request for more or lesstorque to be delivered to the wheels. As another example, the controlssystem can reference transmission shift schedules stored in memory thatcan direct the control system to adjust the operating state of thetransmission in response to particular combinations of operatingconditions identified at 710.

If the answer at 712 is no, the routine can return. Alternatively, ifthe answer at 712 is yes, the transmission actuators that areresponsible for effectuating the prescribed transmission operating stateadjustment can be identified as indicated at 714. For example, toperform a gear change, one, two, three or more actuators can be selectedfor adjustment. At 716, the temperature at the actuators that are to beadjusted can be identified utilizing one or more of the approachespreviously described with reference to FIGS. 3 and 4. For example, thecontrol system can apply a current to the actuator coil and measuringthe resulting voltage, which can be correlated with the temperature atthe actuator. However, in some conditions, the control system canreference the temperature that was previously identified for some or allof the actuators. For example, the control system can utilize theapproaches of FIGS. 3 and 4 to identify the temperature at some or allof the actuators before the transmission adjustment is requested,whereby the identified temperatures can be stored in memory for laterrecall by the control system. In this way, the adjustment to thetransmission state need not be delayed in order to obtain a temperaturemeasurement before adjusting the actuator by application of an actuationcurrent.

At 718, the prescribed adjustment of the transmission operating statecan be performed by varying the current applied to the actuatorsidentified at 714 based on their respective temperatures identified at716. For example, the control system can reference a look-up table ormap stored in memory to identify a base actuation timing for each of theactuators, whereby the base actuation timing can be adjusted based onthe respective temperature identified for each actuator as demonstratedby FIG. 6. Thus, the control system can adjust the timing at which theactuation current is applied to the actuator, the magnitude of theactuation current, and/or the rate of change of the actuator current.Finally, the routine can return.

FIG. 7B shows an approach similar to the approach of FIG. 7A, exceptthat the temperature obtained from a first actuator can be used tocontrol the actuation of a second actuator. In this particular example,the operations shown at 740, 742, and 744 can be the same as thosedescribed by operations 710, 712, and 714, respectively. At 746, thetemperature of at least one other actuator can be identified forcontrolling the actuation of another actuator. As one non-limitingexample, the control system can reference a look-up table stored inmemory to identify one or more actuators that are thermally related tothe actuator that is to be adjusted. In other words, the temperature ofat least one actuator that has been obtained by one or more of theapproaches described with reference to FIGS. 3 and 4 can be used tocontrol the actuation of at least one other actuator. For example, thecontrol system can reference the last identified temperature of anactuator that is physically closest to the actuator that is to beadjusted (e.g. either spatially or by proximity along the fluid circuitwithin the transmission) or the actuator can utilize an averagetemperature obtained from two or more actuators. In this way, theactuation of the actuator need not be delayed in order to obtain thetemperature at the actuator, but the temperature obtained from otheractuators may instead be relied upon to control the application of theactuation current. Thus, the control system can be configured tocorrelate the temperature at a first actuator with the temperature at asecond actuator. At 748, the prescribed transmission adjustment can becarried out by vary the current applied to the actuators identified at744 based on the temperature indication obtained from the otherthermally related actuators identified at 746.

In this way, the approaches of FIGS. 7A and/or 7B can be usedindependently or in conjunction to coordinate actuation events amongvarious actuators of the transmission in order to reduce variations intransmission operating state adjustments that may occur as a result oftemperature fluctuations.

FIG. 8 shows a graph depicting how the shift points of the transmissioncan vary with temperature obtained from an actuator coil. An exampleshift point at which the gear ratio of the transmission can be increasedor decreased is shown at 810 for a first temperature indication obtainedfrom a transmission actuator. A second example shift point at which thegear ratio of the transmission can be increased or decreased is shown at820 for a second temperature indication obtained from the transmissionactuator. In this particular example, shift points 810 and 820 representthe same adjustment to the transmission operating state. For example,both of shift points 810 and 820 represent an adjustment of thetransmission from a first gear ratio to a second gear ratio and canrepresent an upshift or a downshift of the transmission.

As indicated by comparing shift points 810 and 820, the operatingconditions at which the transmission is shifted by the control systemvia at least one actuator can vary based upon the indication oftemperature obtained from at least one actuator of the transmission. Forexample, an operating condition of vehicle speed at which thetransmission is shifted can be different between the two temperatureconditions as indicated by offset 830. The vehicle speed shown along thevertical axis can be obtained by the control system via a speed sensorthat provides an indication of drive wheel speed. Similarly, theoperating condition of engine torque at which the transmission is shiftcan be different between the two temperature conditions as indicated byoffset 840. The engine torque shown along the horizontal axis can beobtained by the control system via a throttle positions sensor, anestimation of engine load, and can be further based on engine speed asmay be obtained from crankshaft speed sensor, etc.

Thus, FIG. 8 shows an example where shift points of the transmission canbe adjusted by the control system based on an indication of temperatureobtained from temperature dependant electrical property of at least oneactuator coil. Note that the various shift points can be stored inmemory at the control system as a look-up table or map for reference.

The example control and estimation routines included herein can be usedwith various engine and/or vehicle system configurations. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1-20. (canceled)
 21. A propulsion system for a vehicle, comprising: apropulsion device configured to provide mechanical work via acrankshaft; a transmission having an input shaft coupled with thecrankshaft and an output shaft, wherein said transmission includes aplurality of selectable gear ratios between the input and output shaft;at least one drive wheel coupled with the output shaft; an actuationdevice configured to adjust the selected gear ratio of the transmission;and a control system configured to adjust an electrical signal providedto the actuation device to obtain an indication of a temperaturedependent electrical parameter of the actuation device and to adjust theselected gear ratio of transmission by varying a timing and level of thesignal provided to the actuation device in response to said indication.22. The system of claim 21, wherein said actuation device includes anactuator coil and wherein said indication of the temperature dependantelectrical parameter includes a resistance of the actuator coil.
 23. Thesystem of claim 21, wherein said control system is further configuredto: responsive to a first indication of the temperature dependentelectrical parameter of the actuation device, adjust the selected gearratio of the transmission from a first gear ratio to a second gear ratioat a first operating condition; and responsive to a second indication ofthe temperature dependent electrical parameter of the actuation devicedifferent than the first indication, adjust the selected gear ratio ofthe transmission from the first gear ratio to the second gear ratio at asecond operating condition different than the first operating condition.24. The system of claim 23, wherein the first operating conditionincludes a first speed of the drive wheel and the second operatingcondition includes a second speed of the drive wheel different than thefirst speed.
 25. The system of claim 24, wherein the first operatingcondition further includes a first level of torque provided by thepropulsion device via the crankshaft and the second operating conditionfurther includes a second level of torque provided by the propulsiondevice via the crankshaft different than the first level of torque. 26.The system of claim 21, wherein the propulsion device includes aninternal combustion engine.
 27. The system of claim 21, wherein thepropulsion device includes an electrically powered drive motor.
 28. Amethod of operating a vehicle transmission including a first and asecond actuator, comprising: performing a transmission shift byactuating a first transmission element via the first actuator andactuating a second transmission element via the second actuator; andvarying a timing and magnitude of actuation of the first actuatorrelative to the second actuator based on temperature indications oftemperature dependant electrical properties of the first and actuators.29. The method of claim 28, further comprising: obtaining a firsttemperature indication based on a temperature dependant electricalproperty of the first actuator; obtaining a second temperatureindication based on a temperature dependant electrical property of thesecond actuator; and varying said timing of actuation of the firsttransmission element relative to the second transmission element basedon the first temperature indication and the second temperatureindication.
 30. The method of claim 29 further comprising, varying thetiming of actuation of the first transmission element relative to thesecond transmission element based on a comparison of the first andsecond temperature indications.
 31. The method of claim 29, wherein thetemperature dependant electrical property of the first actuator includesa resistance of a first actuator coil of the first actuator and thetemperature dependant electrical property of the second actuatorincludes a resistance of a second actuator coil of the second actuator.32. A method of operating a vehicle transmission including a firsttransmission actuator configured to adjust a transmission operatingstate, comprising: obtaining a first temperature indication of the firstactuator based on an electrical property of the first actuator; issuinga first command signal to the first actuator to adjust the transmissionoperating state; and varying a timing and magnitude of the first commandsignal responsive to the first temperature indication.
 33. The method ofclaim 32, wherein said varying the parameter of the first command signalfurther includes varying a rate of increase or decrease of the firstcommand signal.
 34. The method of claim 32, wherein the first commandsignal indicates a level of current to be applied to a first actuatorcoil of the first actuator.
 35. The method of claim 32, wherein theoperating state of the transmission includes a gear ratio between aninput shaft and an output shaft of the transmission and wherein theelectrical property includes an electrical resistance of an actuatorcoil of the first actuator.
 36. The method of claim 32, wherein thetransmission includes at least a second transmission actuator configuredto further adjust the operating state of the transmission and whereinthe method further comprises: obtaining a second temperature indicationof the second actuator based on an electrical property of the secondactuator; issuing a second command signal to the second actuator tofurther adjust the transmission operating state; and varying a timingand magnitude of the second command signal responsive to the secondtemperature indication.
 37. The method of claim 36, further comprising,varying the timing and magnitude of the second command signal relativeto the timing and magnitude of the first command signal based on atemperature difference between the first temperature indication and thesecond temperature indication.